Technical Field
The present invention relates to a controller having an auto-tuning function, a control method in the controller, and a control program for implementing the controller.
Related Art
Feedback control systems including PID control systems are now used in a variety of applications such as temperature control, speed control, and position control. In such a feedback control system, in order to enhance responsiveness to a change of a target value and convergence for disturbance, it is important to optimize control parameters such as proportional gain, integral time, and derivative time in accordance with a controlled object.
It is, however, difficult for users having no knowledge on feedback control systems to optimize control parameters. Auto-tuning function for automatically optimizing such control parameters have therefore been developed and put into practice. As typical examples of such auto-tuning function, the step response method, the ultimate sensitivity method (see Non PTD 1), the limit cycle method (see PTDs 1 and 2), and other methods are known.
Specifically, Japanese Patent Laying-Open No. 05-289704 (PTD 1) discloses a heating/cooling controller having two kinds of, namely, heating and cooling, PID computation functions. This heating/cooling controller has heating and cooling auto-tuning functions. Japanese Patent Laying-Open No. 2004-227062 (PTD 2) discloses a heat/cool control technique in which temperature control is performed by appropriately switching between a heat mode for outputting a manipulated value to a heating actuator and a cool mode for outputting a manipulated value to a cooling actuator. This heat/cool control technique includes a limit cycle auto-tuning method in which a control parameter is adjusted by producing limit cycles having a constant manipulated value amplitude.